Process for hydrosonically area thinning thin sheet materials

ABSTRACT

A method for forming thinned areas in a thin sheet material. The method includes the steps of (1) placing the thin sheet material on a pattern anvil having a pattern of raised areas wherein the height of the raised areas is generally less than the thickness of the sheet material; (2) conveying the sheet material, while placed on the pattern anvil, through an area where a fluid is applied to the sheet material; and (3) subjecting the sheet material to a sufficient amount of ultrasonic vibrations in the area where the fluid is applied to the sheet material to area thin the sheet material in a pattern generally the same as the pattern of raised areas on the pattern anvil. In some embodiments, the thinned areas may be micro areas.

This application is a divisional application of application Ser. No.07/767,727 filed on Sep. 30, 1991, now U.S. Pat. No. 5,314,737.

RELATED APPLICATIONS

U.S. application Ser. No. 07/767,727 is one of a group of applicationswhich are being filed on the same date Sep. 30, 1991. It should be notedthat this group of applications includes U.S. patent application Ser.No. 07/769,050, entitled "Hydrosonically Microapertured Thin ThermosetSheet Materials" in the names of Lee K. Jameson and Bernard Cohen; U.S.patent application Ser. No. 07/769,047, entitled "HydrosonicallyMicroapertured Thin Thermoplastic Sheet Materials" in the names ofBernard Cohen and Lee K. Jameson; U.S. patent application Ser. No.07/768,782, entitled "Pressure Sensitive Valve System and Process ForForming Said System" in the names of Lee K. Jameson and Bernard Cohen;U.S. patent application Ser. No. 07/768,494, entitled "HydrosonicallyEmbedded Soft Thin Film Materials and Process For Forming SaidMaterials" in the names of Bernard Cohen and Lee K. Jameson; U.S. patentapplication Ser. No. 07/768,494, entitled "Hydrosonically MicroaperturedThin Naturally Occurring Polymeric Sheet Materials and Method of Makingthe Same" in the names of Lee K. Jameson and Bernard Cohen; U.S. patentapplication Ser. No. 07/769,048, now abandoned, entitled "HydrosonicallyMicroapertured Thin Metallic Sheet Materials" in the names of BernardCohen and Lee K. Jameson; U.S. patent application Ser. No. 07/769,045,entitled "Process For Hydrosonically Microaperturing Thin SheetMaterials" in the names of Lee K. Jameson and Bernard Cohen; and U.S.patent application Ser. No. 07/767,727, entitled "Process ForHydrosonically Area Thinning Thin Sheet Materials" in the names ofBernard Cohen and Lee K. Jameson. All of these applications are herebyincorporated by reference.

FIELD OF THE INVENTION

The field of the present invention encompasses processes for areathinning thin sheet materials in a generally uniform pattern and thearea thinned thin sheet materials formed thereby.

BACKGROUND OF THE INVENTION

Ultrasonics is basically the science of the effects of sound vibrationsbeyond the limit of audible frequencies. Ultrasonics has been used in awide variety of applications. For example, ultrasonics has been used for(1) dust, smoke and mist precipitation; (2) preparation of colloidaldispersions; (3) cleaning of metal parts and fabrics; (4) frictionwelding; (5) the formation of catalysts; (6) the degassing andsolidification of molten metals; (7) the extraction of flavor oils inbrewing; (8) electroplating; (9) drilling hard materials; (10) fluxlesssoldering and (10) nondestructive testing such as in diagnosticmedicine.

The object of high power ultrasonic applications is to bring about somepermanent physical change in the material treated. This process requiresthe flow of vibratory power per unit of area or volume. Depending on theapplication, the power density may range from less than a watt tothousands of watts per square centimeter. Although the originalultrasonic power devices operated at radio frequencies, today mostoperate at 20-69 kHz.

The piezoelectric sandwich-type transducer driven by an electronic powersupply has emerged as the most common source of ultrasonic power: theoverall efficiency of such equipment (net acoustic power perelectric-line power) is typically greater than 70%. The maximum powerfrom a conventional transducer is inversely proportional to the squareof the frequency. Some applications, such as cleaning, may have manytransducers working into a common load.

other, more particular areas where ultrasonic vibratory force has beenutilized are in the areas of thin nonwoven webs and thin films. Forexample, ultrasonic force has been use to bond or weld nonwoven webs.See, for example, U.S. Pat. Nos. 3,575,752 to Carpenter, 3,660,186 toSager et al., 3,966,519 to Mitchell et al. and 4,605,454 to Sayovitz etal. which disclose the use of ultrasonics to bond or weld nonwoven webs.U.S. Pat. No. 3,488,240 to Roberts, describes the use of ultrasonics tobond or weld thin films such as oriented polyesters.

Ultrasonic force has also been utilized to aperture nonwoven webs. See,for example, U.S. Pat. Nos. 3,949,127 to Ostermeier et al. and 3,966,519to Mitchell et al.

Lastly, ultrasonic force has been used to aperture thin film material.See, for example, U.S. Pat. No. 3,756,880 to Graczyk.

Other methods for the aperturing of thin film have been developed. Forexample, U.S. Pat. No. 4,815,714 to Douglas discusses the aperturing ofa thin film by first abrading the film, which is in filled andunoriented form, and then subjecting the film to corona dischargetreatment.

One of the difficulties and obstacles in the use of ultrasonic force inthe formation of apertures in materials is the fact that control of theamount of force which is applied was difficult. This lack of controlresulted in the limitation of ultrasonic force to form large aperturesas opposed to small microapertures. Such an application is discussed inU.K. patent application number 2,124,134 to Blair. One of the possiblereasons that ultrasonics has not found satisfactory acceptance in thearea of microaperture formation is that the amount of vibrational energyrequired to form an aperture often resulted in a melt-through of thefilm.

As has previously been stated, those in the art had recognized thatultrasonics could be utilized to form apertures in nonwoven webs. See,U.S. patent to Mitchell, et al,. Additionally, the Mitchell et al.patent discloses that the amount of ultrasonic energy being subjected toa nonwoven web could be controlled by applying enough of a fluid to thearea at which the ultrasonic energy was being applied to the nonwovenweb so that the fluid was present in uncombined form. Importantly, theMitchell, et al. patent states that the fluid is moved by the action ofthe ultrasonic force within the nonwoven web to cause aperture formationin the web by fiber rearrangement and entanglement. The Mitchell et al.patent also states that, in its broadest aspects, since these effectsare obtained primarily through physical movement of fibers, the methodof their invention may be utilized to bond or increase the strength of awide variety of fibrous webs.

While the discovery disclosed in the Mitchell et al. patent, no doubt,was an important contribution to the art, it clearly did not address thepossibility of area thinning of nonfibrous thin sheet materials or thinsheet materials having fibers in such a condition that they could not bemoved or rearranged. This fact is clear because the Mitchell et al.patent clearly states the belief that the mechanism of apertureformation depended upon fiber rearrangement. Of course, such thin sheetmaterials do not have fibers which can be rearranged. Accordingly, itcan be stated with conviction that the applicability of a method forarea thinning such thin sheet materials by the application of ultrasonicenergy in conjunction with a fluid at the point of application of theultrasonic energy to the sheet material was not contemplated by theMitchell et al. patent. Moreover, the Mitchell et al. patent teachesaway from such an application because the patent states the belief thataperture formation (physical effects) requires the presence of fibers tobe rearranged.

Another area of interest to the present invention is the area of barrierfabrics. Barrier fabrics are utilized in a variety of areas. Forexample, chemical workers sometimes wear garments made from a barrierfabric which seeks to protect the worker from harmful materials which hemay become exposed to. Likewise, operating room personnel typically weargarments which are designed to protect the patient from germs that thepersonnel may carry and also protect the operating room personnel fromgerms, viruses etc. that the patient may harbor. While many barrierfabrics have been designed, one of the more difficult aspects of thecreation of barrier fabrics which are to be used to make garments is tomake the fabric "breathable". In other words, for the comfort of thewearer, it is highly desirable for the fabric to act as a barrier to thepotentially harmful substance that it is designed to block while stillallowing the passage of air and water vapor. Otherwise, the garment maywell quickly turn into a "hot box". Accordingly, it has long been a goalof those in the art to produce a barrier fabric which is "breathable"but, a the same time, provides adequate protection against the harmfulsubstance which is to be maintained at a distance.

DEFINITIONS

As used herein the term "sheet material" refers to a generally nonporousitem that can be arranged in generally planar configuration which, in anunthinned state, prior to being modified in accordance with the presentinvention, has a hydrostatic pressure (hydrohead) of at least about 100centimeters of water when measured in accordance with Federal TestMethod NO. 5514, standard no. 191A. This term is also intended toinclude multilayer materials which include at least one such sheet as alayer thereof. As used herein the term "thin sheet material" refers to asheet material having an average thickness generally of less than aboutten (10) mils. Average thickness is determined by randomly selectingfive (5) locations on a given sheet material, measuring the thickness ofthe sheet material at each location to the nearest 0.1 mil, andaveraging the five values (sum of the five values divided by five).

As used herein the term "mesh count" refers to the number which is theproduct of the number of wires in a wire mesh screen in both the machine(MD) and cross-machine (CD) directions in a given unit area. Forexample, a wire mesh screen having 100 wires per inch in the machinedirection and 100 wires per inch in the cross machine direction wouldhave a mesh count of 10,000 per square inch. As a result of theinterweaving of these wires, raised areas are present on both sides ofthe mesh screen. The number of raised areas on one side of such a wiremesh screen is generally one-half of the mesh count.

As used herein the term "microarea" refers to an area which has an areaof less than about 100,000 square micrometers. The area of the microareais to be measured by microscopic enlargement.

As used herein the terms "thinned area" or "area thinned" refer to anarea in a sheet material having a thickness which is at least about 25percent less than the thickness of the surrounding sheet material. Forexample, the thinned area may have a thickness which is at least about50 percent less than the thickness of the surrounding sheet material.More particularly, the thinned area may have a thickness which is atleast about 75 percent less than the surrounding sheet material. Evenmore particularly, the thinned area may have a thickness which is atleast about 90 percent less than the surrounding sheet material. Becausethe thinning process may not be exactly uniform, the thickness of athinned area is to be measured at its thinnest point.

As used herein the term "ultrasonic vibrations" refers to vibrationshaving a frequency of at least about 20,000 cycles per second. Thefrequency of the ultrasonic vibrations may range from about 20,000 toabout 400,000 cycles per second.

As used herein the terms "polymer" or "polymeric" refer to amacromolecule formed by the chemical union of five (5) or more identicalcombining units called monomers.

As used herein the term "naturally occurring polymeric material" refersto a polymeric material which occurs naturally. The term is also meantto include materials, such as cellophane, which can be regenerated fromnaturally occurring materials, such as, in the case of cellophane,cellulose. Examples of such naturally occurring polymeric materialsinclude, without limitation, (1) polysaccharides such as starch,cellulose, pectin, seaweed gums (such as agar, etc.), vegetable gums(such as arabic, etc.); (2) polypeptides; (3) hydrocarbons such asrubber and gutta percha (polyisoprene) and (4) regenerated materialssuch as cellophane or chitosan. As used herein the terms "metal" or"metallic" refer to an element that forms positive ions when itscompounds are in solution and whose oxides form hydroxides rather thatacids with water.

As used herein the term "thermoset material" refers to a high polymerthat solidifies or "sets" irreversibly when heated. This property isalmost invariably associated with a cross-linking reaction of themolecular constituents induced by heat or irradiation. In many cases, itis necessary to add "curing" agents such as organic peroxides or (in thecase of natural rubber) sulfur to achieve cross-linking. For examplethermoplastic linear polyethylene can be cross-linked to a thermosettingmaterial either by radiation or by chemical reaction. A generaldiscussion of cross-linking can be found at pages 331 to 414 of volume 4of the Encyclopedia of Polymer Science and Technology, Plastics, Resins,Rubbers, Fibers published by John Wiley & Sons, Inc. and copyrighted in1966. This document has a Library of Congress Catalog Card No. of64-22188. Phenolics, alkylds, amino resins, polyesters, epoxides, andsilicones are usually considered to be thermosets. The term is alsomeant to encompass materials where additive-induced cross-linking ispossible, e.g. cross-linked natural rubber.

One method for determining whether a material is "cross-linked" andtherefore a thermoset material, is to reflux the material in boilingtoluene, xylene or another solvent, as appropriate, for forty (40)hours. If a weight percent residue of at least 5 percent remains thematerial is deemed to be cross-linked. Another procedure for determiningwhether a material is cross-linked vel non is to reflux 0.4 gram of thematerial in boiling toluene or another appropriate solvent, for examplexylene, for twenty (20) hours. If no insoluble residue (gel) remains thematerial may not be cross-linked. However, this should be confirmed bythe "melt flow" procedure below. If, after twenty (20) hours ofrefluxing insoluble residue (gel) remains the material is refluxed underthe same conditions for another twenty (20) hours. If more than 5 weightpercent of the material remains upon conclusion of the second refluxingthe material is considered to be cross-linked. Desirably, a least tworeplicates are utilized. Another method whereby cross-linking vel nonand the degree of cross-linking can be determined is by ASTM-D-2765-68(Reapproved 1978). Yet another method for determining whether a materialis cross-linked vel non is to determine the melt flow of the material inaccordance with ASTM D 1238-79 at 230° Centigrade while utilizing a21,600 gram load. Materials having a melt flow of greater than 75 gramsper ten minutes shall be deemed to be non-cross-linked. This methodshould be utilized to confirm the "gel" method described above wheneverthe remaining insoluble gel content is less than 5% since somecross-linked materials will evidence a residual gel content of less than5 weight percent.

As used herein the term "thermoplastic material" refers to a highpolymer that softens when exposed to heat and returns to its originalcondition when cooled to room temperature. Natural substances whichexhibit this behavior are crude rubber and a number of waxes. Otherexemplary thermoplastic materials include, without limitation, polyvinylchloride, polyesters, nylons, fluorocarbons, linear polyethylene such aslinear low density polyethylene, polyurethane prepolymer, polystyrene,polypropylene, polyvinyl alcohol, caprolactams, and cellulosic andacrylic resins.

As used herein the term "hydrosonics" refers to the application ofultrasonic vibrations to a material where the area of such applicationhas had a liquid applied thereto to the extent that the liquid ispresent in sufficient quantity to generally fill the gap between the tipof the ultrasonic horn and the surface of the material.

OBJECTS OF THE INVENTION

Accordingly, it is a general object of the present invention to providea process for area thinning thin sheet materials in a generally uniformpattern.

Yet a further object of the present invention is to provide thin sheetmaterials which have been area thinned is a generally uniform pattern.

Still further objects and the broad scope of applicability of thepresent invention will become apparent to those of skill in the art fromthe details given hereinafter. However, it should be understood that thedetailed description of the presently preferred embodiments of thepresent invention is given only by way of illustration because variouschanges and modifications well within the spirit and scope of theinvention will become apparent to those of skill in the art in view ofthis detailed description.

SUMMARY OF THE INVENTION

In response to the forgoing problems and difficulties encountered bythose in the art, we have developed a method for forming thinned areasin a thin sheet material having a thickness of about 10 mils or less.The method includes the steps of: (a) placing the thin sheet material ona pattern anvil having a pattern of raised areas where the height of theraised areas is generally less than the thickness of the thin sheetmaterial; (b) conveying the thin sheet material, while placed on thepattern anvil, through an area where a fluid is applied to the thinsheet material; and (c) subjecting the thin sheet material to ultrasonicvibrations in the area where the fluid is applied to the thin sheetmaterial. As a result of this method the thin sheet material is areathinned in a pattern generally the same as the pattern of raised areason the pattern anvil.

In some embodiments the fluid may be selected from the group includingone or more of water, mineral oil, a chlorinated hydrocarbon, ethyleneglycol or a solution of 50 volume percent water and 50 volume percent 2propanol. For example, the chlorinated hydrocarbon may be selected fromthe group including 1,1,1 trichloroethane or carbon tetrachloride.

In some embodiments the thin sheet material is area thinned with athinned area density of at least about 1,000 thinned areas per squareinch. For example, the thin sheet material may be area thinned with athinned area density of at least about 5,000 thinned areas per squareinch. More particularly, the thin sheet material may be area thinned,with a thinned area density of at least about 20,000 thinned areas persquare inch. Even more particularly, the thin sheet material may be areathinned with a thinned area density of at least about 90,000 thinnedareas per square inch. Yet even more particularly, the thin sheetmaterial may be area thinned with a thinned area density of at leastabout 160,000 thinned areas per square inch.

In some embodiments, the thinned areas are microareas. For example, thearea of each of the thinned microareas may generally range from at leastabout 10 square micrometers to about 100,000 square micrometers. Moreparticularly, the area of each of the thinned microareas generally mayrange from at least about 10 square micrometers to about 1,000 squaremicrometers. Even more particularly, the area of each of the thinnedmicroareas may generally range from at least about 10 square micrometersto about 100 square micrometers.

In some embodiments, the pattern anvil may be a mesh screen. In otherembodiments the pattern anvil may be a flat plate with raised areas. Ineven other embodiments, the pattern anvil may be a cylindrical rollerwith raised areas.

In some embodiments the thin sheet material is area thinned only inselected predesignated areas.

In some embodiments, the thin sheet material is subjected to a least tosteps (b) and (c) more than one time.

In some embodiments the height of the raised areas is greater than thethickness of the thin sheet material and the thin sheet material isformed from a material having a resilience such that the thin sheetmaterial is area thinned as opposed to being apertured by theapplication of hydrosonic energy.

In some embodiments, the mechanism for subjecting the sheet material toultrasonic vibrations is an ultrasonic horn where the ultrasonic hornhas a tip which may be aligned, with respect to the thin sheet material,at an angle of from about 5 degrees to about 15 degrees. For example,the tip of the ultrasonic horn may be aligned, with respect to the thinsheet material, at an angle of from about 7 to about 13 degrees. Moreparticularly, the tip of the ultrasonic horn may be aligned, withrespect to the thin sheet material, at an angle of from about 9 to about11 degrees.

The invention is also directed to a thin sheet material having at leastabout 1,000 thinned areas per square inch. For example, the thin sheetmaterial may have a least about 5,000 thinned areas per square inch.More particularly, the thinned sheet material may have at least about20,000 thinned areas per square inch. Even more particularly, thethinned sheet material may have at least about 90,000 thinned areas persquare inch. Yet even more particularly, the thinned sheet material mayhave at least about 160,000 thinned areas per square inch.

In some embodiments, the average thickness of the sheet material may beat least about 0.25 mil. For example, the average thickness of the sheetmaterial may range from about 0.25 mil to about 5 mils. Moreparticularly, the average thickness of the sheet material may range fromabout 0.25 mil to about 2 mils. Yet even more particularly, the averagethickness of the sheet material may range from about 0.5 mil to about 1mil.

In some embodiments the thinned areas are microareas. For example thearea of each of the thinned areas may generally range from at leastabout 10 square micrometers to about 100,000 square micrometers. Moreparticularly, the area of each of the thinned areas may range from atleast about 10 square micrometers to about 10,000 square micrometers.Even more particularly, the area of each of the thinned areas may rangefrom at least about 10 square micrometers to about 5,000 squaremicrometers. Yet even more particularly, the area of each of the thinnedareas may range from at least about 10 square micrometers to about 1,000square micrometers.

In some embodiments the thinned sheet material is breathable and thewater vapor transmission rate of the thinned sheet material is at leastabout 200 grams per square meter per day. For example, the water vaportransmission rate of the thinned sheet material may be at least at leastabout 500 grams per square meter per day. More particularly, the watervapor transmission rate of the thinned sheet material may be at least atleast about 1,000 grams per square meter per day.

THE FIGURES

FIG. 1 is a schematic representation of apparatus which may be utilizedto apply ultrasonic vibrations to thin sheet materials to thin areas inthe thin sheet materials.

FIG. 2 is a cross sectional view of the transport mechanism fortransporting the thin sheet material to the area where it is subjectedto ultrasonic vibrations.

FIG. 3 is a detailed view of the area where the thin sheet material issubjected to ultrasonic vibrations. The area is designated by the dottedcircle in FIG. 1.

FIG. 4 is a cross sectional photomicrograph of a 1 mil thick sheet ofpolyethylene film which has been area thinned in accordance with thepresent invention.

FIG. 5 is a plan view of a thinned area of the film of FIG. 4

FIG. 6 is a scale for use with FIGS. 4 and 5 where each unit representsten (10) microns (micrometers).

FIG. 7 is a cross sectional photomicrograph of a 1.4 mil thick sheet ofDupont film sold under the trade designation "Evlon" which has been areathinned in accordance with the present invention.

FIG. 8 is a plan view of a thinned area of the film of FIG. 7.

FIG. 9, is a scale for use with FIGS. 7 and 8 where each unit representsten (10) microns (micrometers).

FIG. 10 is a cross sectional photomicrograph of a 0.8 mil thick sheet ofcellophane sold under the trade designation Flexel V-58 which has beenarea thinned in accordance with the present invention.

FIG. 11 is a plan view of a thinned area of the film of FIG. 10.

FIG. 12 is a scale for use with FIGS. 10 and 11 where each unitrepresents ten (10) microns (micrometers).

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the figures where like reference numerals represent likestructure and, in particular to FIG. 1 which is a schematicrepresentation of an apparatus which can carry out the method of thepresent invention, it can be seen that the apparatus is generallyrepresented by the reference numeral 10. In operation, a supply roll 12of a thin sheet material 14 to be area thinned is provided. As has beenpreviously stated, the term thin sheet material refers to sheetmaterials which have an average thickness of about ten (10) mils orless. Additionally, generally speaking, the average thickness of thethin sheet material 14 will be at leas about 0.25 mil. For example, theaverage thickness of the thin sheet 14 material may range from about0.25 mil to about 5 mils. More particularly, the average thickness ofthe thin sheet material 14 may range from about 0.25 mil to about 2mils. Even more specifically, the average thickness of the thin sheetmaterial 14 may range from about 0.5 mil to about 1 mil.

The thin sheet material 14 may be formed from a wide variety ofmaterials. For example, the thin sheet material may be formed from athermoplastic film. The thermoplastic film may be formed from a materialselected from the group including one or more polyolefins,polyurethanes, polyesters, A-B-A' block copolymers where A and A' areeach a thermoplastic polymer endblock which includes a styrenic moietyand where A may be the same thermoplastic polymer endblock as A', andwhere B is an elastomeric polymer midblock such as a conjugated diene ora lower alkene or ethylene vinyl acetate copolymer. The polyolefin maybe selected from the group including one or more of linear low densitypolyethylene, polyethylene or polypropylene. The thermoplastic film maybe a filled film with the filled film being selected form the groupincluding a polyethylene film filed with starch, titanium dioxide, wax,carbon or calcium carbonate.

Alternatively, the sheet material may be a thermoset film. The thermosetfilm may be formed from a material selected from the group including ofone or more cross-linked polyesters, cross-linked natural rubber orcross-linked dimethyl siloxane.

In other embodiments the sheet material may be a metal. For example, themetal may be selected from the group including aluminum, copper, gold,silver, zinc, lead, iron or platinum.

In even further embodiments the sheet material may be a naturallyoccurring polymeric material. For example, the naturally occurringpolymeric material may be selected from the group including cellophane,cellulose acetate, collagen or carrageenan.

Other appropriate sheet materials will be apparent to those of skill inthe art after review of the present disclosure.

The thin sheet material 14 is transported to a first nip 16 formed by afirst transport roll 18 and a first nip roller 20 by the action of anendless transport mechanism 22 which moves in the direction indicated bythe arrow 24. The transport mechanism 22 is driven by the rotation ofthe first transport roller 18 in conjunction with a second transportroller 26 which, in turn, are driven by a conventional power source, notshown.

FIG. 2 is a cross sectional view of the transport mechanism 22 takenalong lines A--A in FIG. 1. FIG. 2 discloses that the transportmechanism 22 includes a heavy duty transport wire mesh screen 28 usuallyhaving a mesh count of less than about 400 (i.e. less than about 20wires per inch by 20 wires per inch mesh screen if machine direction(MD) and cross machine direction (CD) wire count is the same). Heavyduty mesh wire screens of this type may be made from a variety ofmaterials such as, for example, metals, plastics, nylons or polyesters,and are readily available to those in the art. Located above andattached to the transport screen 28 is an endless flat shim plate 30.The shim plate 30 desirably is formed from stainless steel. However,those of skill in the art will readily recognize that other materialsmay be utilized. Located above and attached to the shim plate 30 is afine mesh wire pattern screen 32 usually having a mesh count of at leastabout 2,000 per square inch (i.e. at least a 45 wires per MD inch by 45wires per CD inch mesh screen if MD and CD wire count is the same). Finemesh wire screens of this type are readily available to those in theart. The fine mesh wire screen 32 has raised areas or knuckles 34 whichperform the function of a pattern anvil as will be discussed later.

From the first nip 16 the thin sheet material 14 is transported by thetransport mechanism 22 over a tension roll 36 to an area 38 (defined inFIG. 1 by the dotted lined circle) where the thin sheet material 14 issubjected to ultrasonic vibrations.

The assembly for subjecting the thin sheet material 14 to the ultrasonicvibrations is conventional and is generally designated at 40. Theassembly 40 includes a power supply 42 which, through a power control44, supplies power to a piezoelectric transducer 46. As is well known inthe art, the piezoelectric transducer 46 transforms electrical energyinto mechanical movement as a result of the transducer's vibrating inresponse to an input of electrical energy. The vibrations created by thepiezoelectric transducer 46 are transferred, in conventional manner, toa mechanical movement booster or amplifier 48. As is well known in theart, the mechanical movement booster 48 may be designed to increase theamplitude of the vibrations (mechanical movement) by a known factordepending upon the configuration of the booster 48. In furtherconventional manner, the mechanical movement (vibrational energy) istransferred from the mechanical movement booster 48 to a conventionalknife edge ultrasonic horn 50. It should be realized that other types ofultrasonic horns 50 could be utilized. For example, a rotary typeultrasonic horn could be used. The ultrasonic horn 50 may be designed toeffect yet another boost or increase in the amplitude of the mechanicalmovement (vibrations) which is to be applied to the thin sheet material14. Lastly, the assembly includes an actuator 52 which includes apneumatic cylinder, not shown. The actuator 52 provides a mechanism forraising and lowering the assembly 40 so that the tip 54 of theultrasonic horn 50 can apply tension to the transport mechanism 22 uponthe assembly 40 being lowered. It has been found that it is necessary tohave some degree of tension applied to the transport mechanism 22 uponthe lowering of the assembly for proper application of vibrationalenergy to the thin sheet material 14 to form thinned areas in the thinsheet material 14. One desirable aspect of this tensioned arrangement isthat the need to design a finely toleranced gap between the tip 54 ofthe horn 50 and the raised areas or knuckles 34 of the fine mesh wirescreen 32 is not necessary.

FIG. 3 is a schematic representation of the area 38 where the ultrasonicvibrations are applied to the thin sheet material 14. As can be seen inFIG. 3, the transport mechanism 22 forms an angle 56 with the tip 54 ofthe ultrasonic horn 50. While some area thinning will occur if the angle56 is as great as 45 degrees, it has been found that it is desirable forthe angle 56 to range from about 5 degrees to about 15 degrees. Forexample, the angle 56 may range from about 7 to about 13 degrees. Moreparticularly, the angle 56 may range from about 9 to about 11 degrees.

FIG. 3 also illustrates that the transport mechanism 22 is supportedfrom below by the first tension roll 36 and a second tension roll 58.Positioned somewhat prior to the tip 54 of the ultrasonic horn 50 is aspray nozzle 60 which is configured to apply a fluid 62 to the surfaceof the thin sheet material 14 just prior to the sheet material's 14being subjected to ultrasonic vibrations by the tip 54 of the ultrasonichorn 50. The fluid 62 desirably may be selected from the group includingone or more of water, mineral oil, a chlorinated hydrocarbon, ethyleneglycol or a solution of 50 volume percent water and 50 volume percent 2propanol. For example, in some embodiments the chlorinated hydrocarbonmay be selected from the group including 1,1,1 trichloroethane or carbontetrachloride. It should be noted that the wedge-shaped area 64 formedby the tip 54 of the ultrasonic horn 50 and the transport mechanism 22should be subjected to a sufficient amount of the fluid 62 for the fluid62 to act as both a heat sink and a coupling agent for the mostdesirable results. Positioned below the transport mechanism 22 in thearea where the tip 54 of the ultrasonic horn 50 is located is a fluidcollection tank 66. (See FIG. 1.) The fluid collection tank 66 serves tocollect fluid 62 which has been applied to the surface of the thin sheetmaterial 14 and which has been driven over the edges of the transportmechanism 22 by the action of the vibrations of the tip 54 of theultrasonic horn 50. Fluid 62 which is collected in the collection tank66 is transported by tubing 68 to a fluid holding tank 70.

FIG. 1 illustrates that the fluid holding tank 70 contains a pump 72which, by way of additional tubing 74, supplies the fluid 62 to thefluid spray nozzle 60. Accordingly, the fluid 62 may be re-cycled for aconsiderable period of time.

While the mechanism of action may not be fully understood and thepresent application should not be bound to any particular theory ormechanism of action, it is believed that the presence of the fluid 62 inthe wedge-shaped area 64 during operation of the ultrasonic horn 50accomplishes two separate and distinct functions. First, the presence ofthe fluid 62 allows the fluid 62 to act as a heat sink which allows theultrasonic vibrations to be applied to the thin sheet material 14without the thin sheet material 14 being altered or destroyed as bymelting. Secondly, the presence of the fluid 62 in the wedge-shaped area64 allows the fluid 62 to act as a coupling agent in the application ofthe vibrations from the ultrasonic horn 50 to the thin sheet material14.

It has been discovered that the action of the ultrasonic horn 50 on thethin sheet material 14 thins areas in the thin sheet material 14 inspite of the fact that there are no fibers to re-arrange as was the casein Mitchell et al. The thinned areas are punched into the thin sheetmaterial 14 in the pattern of the raised areas or knuckles 34 of thefine mesh wire pattern screen 32. Generally, the number of thinned areasproduced will be equal to the number of raised areas or knuckles 34 onthe upper surface of the fine mesh wire screen 32. That is, the numberof thinned areas will generally be one-half the mesh count of a givenarea of pattern screen 32. For example, if the pattern screen 32 is 100wires per inch MD by 100 wires per inch CD, the total number of knucklesor raised areas 34 on one side of the pattern wire per square inch 32will be 100 times 100 divided by 2. This equals 5,000 thinned areas persquare inch. For a 200 wires per inch MD by 200 wires per inch CDpattern screen 32 the calculation yields 20,000 thinned areas per squareinch. Depending somewhat on the thickness of the thin sheet material 14,at a mesh count of about 90,000 (300 wires per inch MD by 300 wires perinch CD) the wires are so thin as to allow the knuckles 34 on both sidesto area thin the thin sheet material 14 if sufficient force is applied.Thus, a 300 wires per inch MD by 300 wires per inch CD mesh screenyields 90,000 thinned areas per square inch; for a 400 wires per inch MDby 400 wires per inch CD mesh--160,000 thinned areas per square inch. Ofcourse the MD and CD wire count of the wire mesh screen does not have tobe the same.

Also as a result of the area thinning process the edge length of thethin sheet material may be increased by at least about 100 percent ascompared to the sheet's edge length prior to area thinning. For example,the edge length of the thin sheet material may be increased by at leastabout 500 percent as compared to the sheet's edge length prior to areathinning. More particularly, the edge length of the thin sheet materialmay be increased by at least about 1,500 percent as compared to thesheet's edge length prior to area thinning. Even more particularly, theedge length of the thin sheet material may be increased by at leastabout 3,000 percent as compared to the sheet's edge length prior to areathinning.

It should also be noted that the number of thinned areas formed may alsovary with the number of ultrasonic vibrations to which the thin sheetmaterial 14 is subjected per unit area for a given period of time. Thisfactor may be varied in a number of ways. For example, the number andsize of the thinned areas will vary somewhat with the line speed of thethin sheet material 14 as it passes underneath the tip 54 of theultrasonic horn 50. Generally speaking, as line speed increases, firstthe size and depth of the thinned areas decreases and then the number ofthinned areas decreases. As the number of thinned areas decreases theless the pattern of thinned areas resembles the pattern of raised areas34 on the pattern screen 32. The range of line speeds that usuallyyields thinned areas varies with the material utilized to form the thinsheet material 14 and the material used as the fluid 62. Forpolyethylene film having a thickness of about 1 mil, typical line speedswhich are believed to yield thinned areas for a wide variety of fluidsrange from about 14 to about 28 feet per minute. If water is used as thefluid with such polyethylene film, typical line speeds which arebelieved to yield thinned areas range from about 14 to about 28 feet perminute. For cellophane having a thickness of about 0.8 mil, typical linespeeds which are believed to yield thinned areas for a wide variety offluids range from about 12 to about 18 feet per minute. If water is usedas the fluid with cellophane, typical line speeds which usually yieldthinned areas range from about 12 to about 18 feet per minute.

It should be understood that one limitation on the present process isthe degree of elasticity of the thin sheet material 14. If the sheetmaterial is formed from a highly elastic material it may be verydifficult, if not impossible, to area thin the material. This is due tothe fact that, due to extreme resilience, the material will return togenerally its original shape after being transiently thinned. Thus, thethinned areas are initially formed but soon disappear due to the memoryof the highly elastic sheet material.

It is believed that, to some extent, the variations in the number ofthinned areas formed and the size of the thinned areas occurs due to theminute variations in the height of the raised areas or knuckles 34 ofthe fine mesh pattern screen 32. It should be noted that the fine meshpattern screens used to date have been obtained from conventionaleveryday sources such as a hardware store. It is also believed that if apattern screen 32 could be created where all of the raised areas 34 ofthe screen 32 were of exactly the same height these variations wouldonly occur in uniform fashion with variations of line speed.

As was stated above, the area or size of each of the thinned areasformed will also vary with the parameters discussed above. The area ofthe thinned areas will also vary with the area of the raised areas ofthe pattern anvil such as the knuckles 34 on the fine mesh wire screen32. It is believed that the type of material used in forming the thinsheet material 14 will also vary the area of the thinned areas formed ifall other parameters are maintained the same. For example, the softerthe thin sheet material 14, the easier it is to push the thin sheetmaterial 14 through the raised areas of the fine mesh pattern screen 32.Because the raised areas (knuckles) on the fine mesh screen aregenerally pyramidal in shape, the deeper the raised area penetrates thethin sheet material 14, the larger the and thinner the thinned area. Insuch situations the shape of the thinned area will conform generally tothe pyramidal shape of the raised area of the fine mesh screen and thethinned area will be generally pyramidally shaped, in the z direction.As has been previously stated, the area of the thinned area can beapproximately calculated by microscopic enlargement. Usually the heightof the raised areas must be less than the thickness of the thin sheetmaterial 14 for thinned areas to be formed. However, in some situations,when the thin sheet material 14 is formed from a very resilientmaterial, the height of the raised areas may be greater than thethickness of the thin sheet material 14 due to the fact that the thinsheet material will stretch and thin but not aperture.

In some embodiments it may be necessary to subject the thin sheetmaterial 14 to multiple passes through the apparatus 10 in order to thinareas in the thin sheet material 14 to the degree desired. In suchsituations the thin sheet material 14 will initially only be thinned toa slight degree in the pattern of the pattern anvil's raised areas.However, two or more passes through the apparatus 10, with the thinsheet material 14 being aligned in the same configuration with respectto the pattern anvil will yield areas thinned to the degree desired.Essentially what is happening in these situations is that the thin sheetmaterial 14 is repeatedly thinned by repeated application of ultrasonicvibrational force until such time as areas which are thinned to thedesired degree are formed. Care should be taken that the areas are notapertured by repeated application of hydrosonic vibrations. Anotherfeature of the present invention is the fact that the thinned areas canbe formed in a predesignated area or areas of the thin sheet material14. This can be accomplished in a number of ways. For example, the thinsheet material 14 may be subjected to ultrasonic vibrations only atcertain areas of the sheet material, thus, area thinning would occuronly in those areas. Alternatively, the entire thin sheet material couldbe subjected to ultrasonic vibrations with the pattern anvil havingraised areas only at certain locations and otherwise being flat.Accordingly, the thin sheet material 14 would have thinned areas only inthose areas which corresponded to areas on he pattern anvil havingraised areas.

It should also be noted that some limitation exists in the number ofthinned areas which can be formed in a given thin sheet material 14 on asingle application of vibrational energy, i.e. a single pass through theapparatus if a wire mesh screen is used as the pattern anvil. Thisfollows from the fact that the height of the raised areas must besufficient to effect some thinning of the thin sheet material 14 inconjunction with the fact that, generally as the mesh count increasesthe height of the raised areas or knuckles decreases. In suchsituations, if the number of thinned areas desired per unit area isgreater than the number which can be formed in one pass through theapparatus, multiple passes are necessary with the alignment of the thinsheet material 14 with respect to the raised areas being altered orshifted slightly on each pass.

In some embodiments the areas may be micro areas. Generally speaking thearea of each of the thinned microareas is usually greater than about tensquare micrometers. That is the area of each of the thinned microareasmay range from at least about 10 square micrometers to about 100,000square micrometers. For example, the area of each of the formed thinnedmicroareas may generally range from at least about 10 square micrometersto about 10,000 square micrometers. More particularly, the area of eachof the thinned microareas formed may generally range from at least about10 square micrometers to about 1,000 square micrometers. Even moreparticularly, the area of each of the thinned microareas formed maygenerally range from at least about 10 square micrometers to about 100square micrometers.

A number of important observations about the process may now be made.For example, it should be understood that the presence of the fluid 62is highly important to the present inventive process which uses thefluid as a coupling agent. Because a coupling agent is present, thethinned areas are punched into the thin sheet material 14 as opposed tobeing formed by melting. The importance of the fluid 62 is furtherexemplified by the fact that the process has been attempted without theuse of the fluid 62 and was not generally successful. Additionally, thepresence of the shim plate 30 or its equivalent is necessary in order toprovide an anvil mechanism against which the thin sheet material 14 maybe worked, that is thinned, by the action of the tip 54 of theultrasonic horn 50. Because the vibrating tip 54 of the ultrasonic horn50 is acting in a hammer and anvil manner when operated in conjunctionwith the heavy duty wire mesh screen 28/shim plate 30/fine wire mesh 32combination, it should be readily recognized that a certain degree oftension must be placed upon the transport mechanism 22 by the downwarddisplacement of the ultrasonic horn 50. If there is little or no tensionplaced upon the transport mechanism 22, the shim plate 30 cannot preformits function as an anvil and area thinning generally does not occur.Because both the shim plate 30 and the fine mesh pattern wire 32 formthe resistance that the ultrasonic horn 50 works against, they arecollectively referred herein as a pattern anvil combination. It shouldbe easily recognized by those in the art that the function of thepattern anvil can be accomplished by other arrangements than the heavyduty wire mesh screen 28/shim plate 30/fine mesh screen 32 combination.For example, the pattern anvil could be a flat plate with raisedportions acting to direct the area thinning force of the ultrasonic horn50. Alternatively, the pattern anvil could be a cylindrical rollerhaving raised areas. If the pattern anvil is a cylindrical roller withraised areas, it is desirable for the pattern anvil to be wrapped orcoated with or made from a resilient material. Where the pattern anvilis a mesh screen the resiliency is provided by the fact that the screenis unsupported directly below the point of application of ultrasonicvibrations to the mesh screen.

Depending upon the material used to form the sheet material, the degreeof thinning of each thinned area and the number of thinned areas persquare inch of the sheet material, the strength of the sheet materialwill be degraded upon being thinned. The degree of degradation isevidenced by hydrohead testing of the material prior to and afterthinning. Of course, the hydrohead tests the height of a column of waterthat the material can support before failure.

The invention will now be discussed with regard to specific exampleswhich will aid those of skill in the art in a full and completeunderstanding thereof.

EXAMPLE I

A sheet of 1 mil thick polyethylene film was obtained from the McMasterCarr Corporation of Atlanta, Ga. and was cut into a length of about 11inches and a width of about 8.5 inches. The sample was subjected tohydrosonic treatment in accordance with the present invention.

A model 1120 power supply obtained from the Branson Company of Danbury,Conn., was utilized. This power supply, which has the capacity todeliver 1,300 watts of electrical energy, was used to convert 115 volt,60 cycle electrical energy to 20 kilohertz alternating current. ABranson type J4 power level control, which has the ability to regulatethe ultimate output of the model 1120 power supply from 0 to 100%, wasconnected to the model 1120 power supply. In this example, the powerlevel control was set at 100%. The actual amount of power consumed wasindicated by a Branson model A410A wattmeter. This amount was about 900watts.

The output of the power supply was fed to a model 402 piezoelectricultrasonic transducer obtained from the Branson Company. The transducerconverts the electrical energy to mechanical movement. At 100% power theamount of mechanical movement of the transducer is about 0.8micrometers.

The piezoelectric transducer was connected to a mechanical movementbooster section obtained from the Branson Company. The booster is asolid titanium shaft with a length equal to one-half wave length of the20 kilohertz resonant frequency. Boosters can be machined so that theamount of mechanical movement at their output end is increased ordecreased as compared to the amount of movement of the transducer. Inthis example the booster increased the amount of movement and has a gainratio of about 1:2.5. That is, the amount of mechanical movement at theoutput end of the booster is about 2.5 times the amount of movement ofthe transducer.

The output end of the booster was connected to an ultrasonic hornobtained from the Branson Company. The horn in this example is made oftitanium with a working face of about 9 inches by about 1/2 inch. Theleading and trailing edges of the working face of the horn are eachcurved on a radius of about 1/8 inch. The horn step area is exponentialin shape and yields about a two-fold increase in the mechanical movementof the booster. That is, the horn step area has about a 1:2 gain ratio.The combined increase, by the booster and the horn step area, in theoriginal mechanical movement created by the transducer yields amechanical movement of about 4.0 micrometers.

The forming table arrangement included a small forming table which wasutilized to transport and support the sheet of polyethylene to be areathinned. The forming table included two 2-inch diameter idler rollerswhich were spaced about 12 inches apart on the surface of the formingtable. A transport mesh belt encircles the two idler rollers so that acontinuous conveying or transport surface is created. The transport meshbelt is a square weave 20×20 mesh web of 0.020 inch diameter plasticfilaments. The belt is about 10 inches wide and is raised above thesurface of the forming table.

The transducer/booster/horn assembly, hereinafter the assembly, issecured in a Branson series 400 actuator. When power is switched on tothe transducer, the actuator, by means of a pneumatic cylinder with apiston area of about 4.4 square inches, lowers the assembly so that theoutput end of the horn contacts the sheet of polyethylene which is to bearea thinned. The actuator also raises the assembly so that the outputend of the horn is removed from contact with the sheet of polyethylenefilm when the power is switched off.

The assembly is positioned so that the output end of the horn is adaptedso that it may be lowered to contact the transport mesh belt between thetwo idler rollers. An 8-inch wide 0.01-inch thick stainless steel shimstock having a length of about 60 inches was placed on the plastic meshtransport belt to provide a firm support for a pattern screen which isplaced on top of the stainless steel shim. In this example the patternscreen is a 60 by 60 mesh wire size weave stainless steel screen. Thesheet of polyethylene film which was to be area thinned was hen fastenedonto the pattern wire using masking tape.

The forming table arrangement also included a fluid circulating system.The circulating system includes a fluid reservoir tank, a fluidcirculating pump which may conveniently be located within the tank,associated tubing for transporting the fluid from the tank to a slottedboom which is designed to direct a curtain of fluid into the juncture ofthe output end of the horn and sheet of polyethylene which is to be areathinned.

In operation, the assembly was positioned so that the output end of thehorn was at an angle of from about 10 to 15 degrees to the sheet ofpolyethylene to be area thinned. Accordingly, a wedge shaped chamber wasformed between the output end of the horn and the sheet of polyethyleneto be area thinned. It is into this wedge shaped chamber that the fluid,in this example water at room temperature, is directed by the slottedboom.

It should be noted that the actuator was positioned at a height toinsure that, when the assembly is lowered, the downward movement of theoutput end of the horn is stopped by the tension of the transport meshbefore the actuator reaches the limit of its stroke. In this example,actuating pressure was adjusted to 4 pounds per square inch as read on apressure gauge which is attached to the pneumatic cylinder of theactuator. This adjustment results in a total downward force of 17.6pounds. (4 psi times 4.4 square inches of piston area equals 17.6 poundsof force.)

The sequence of operation was (1) the fluid pump was switched on and thearea where the output end of the horn was to contact the sheet ofpolyethylene film was flooded with water: (2) the transport meshconveyor system was switched on and the polyethylene started moving at20 feet per minute; and (3) power to the assembly was supplied and theassembly was lowered so that the output end of the horn contacted thesheet of polyethylene film while the sheet continued to pass under theoutput end of the horn until the end of the sample was reached. Thereading on the A410A wattmeter during the process is an indication ofthe energy required to maintain maximum mechanical movement a the outputend of the horn while working against the combined mass of the fluid,the sheet of polyethylene, the pattern wire, the shim stock, and thetransport wire.

This example yielded an area thinned polyethylene film having a maximumthinned area density of about 1,800 thinned areas per square inch witheach thinned area having an area of about 3,000 square micrometers. Thethickness of each thinned area was about 2 micrometers.

The water vapor transmission rate of this material after thinning wasmeasured as being about 300 grams per square meter per day. Prior tothinning, the water vapor transmission rate of this material wasmeasured as being about zero (0). Accordingly, the thinning processturned a non-breathable material into a breathable material. Thehydrohead of this material prior to thinning was measured as being inexcess of 137 centimeters of water. After thinning in accordance withExample I, the hydrohead was measured as being 103. Thus, the thinnedsheet material retained a good portion of its strength after thinning.

FIG. 4 and 5 are two photomicrographs of the thin sheet material whichis area thinned in accordance with Example I. FIG. 4 is a cross-sectionof the sheet through a thinned area and figures is a top view of athinned area. FIG. 6 is a scale for use with FIGS. 4 and 5 where eachunit represents ten (10) microns (micrometers).

EXAMPLE II

The process of example I was repeated with the exception that a sheet ofa 1.4 mil thick filled film which is loaded with 50-60%, by weight, (40%by volume) calcium carbonate particles obtained from the DuPont ChemicalCompany of Canada under the trade designation "Evlon" was utilized asthe thin sheet material. The line speed of was about 15 feet per minuteas compared to the 20 feet per minute utilized in example I. The actualamount of power consumed was indicated by the Branson model A410Awattmeter as about 800 watts.

This example yielded a microarea thinned sheet having a maximum densityof about 1,800 thinned areas per square inch with each thinned areahaving an area of about 6,000 square micrometers. The thickness of eachthinned area was about 4 micrometers.

The water vapor transmission rate of this material after thinning wasmeasured several times will variable results. That is, after thinning,the water vapor transmission rate was measured as being about 468, 842and 124 grams per square meter per day. Prior to thinning, the watervapor transmission rate of this material was measured as being about93.8 grams per square meter per day. Accordingly, the thinning processsignificantly improved the breathability of this material.

The hydrohead of this material prior to thinning was measured as beingin excess of 137 centimeters of water. After thinning in accordance withExample II, the hydrohead was measured as being 91. Thus, the thinnedsheet material retained a good portion of its strength after thinning.

FIGS. 7 and 8 are contains two photomicrographs of the thin sheetmaterial which is area thinned in accordance with Example II. FIG. 7 isa cross-section of the sheet through a thinned area and FIG. 8 is a topview of a thinned area. FIG. 9 is a scale for us with FIGS. 7 and 8where each unit represents ten (10) microns (micrometers).

EXAMPLE III

The process of example I was repeated with the exception that a sheet ofa 0.8 mil thick sheet of cellophane obtained under the trade name"Flexel V-58" was utilized as the thin sheet material. The line speed ofwas about 4.5 feet per minute as compared to the 20 feet per minuteutilized in example I. The actual amount of power consumed was indicatedby the Branson model A410A wattmeter as about 800 watts. A 250 by 250stainless steel fine mesh screen was used.

This example yielded a microarea thinned cellophane sheet having amaximum density of about 62,500 thinned areas per square inch with eachthinned area having an area of about 650 square micrometers. Thethickness of each thinned area was about 2 micrometers.

The water vapor transmission rate of this material after thinning wasmeasured as being about 200 grams per square meter per day. Prior tothinning, the water vapor transmission rate of this material wasmeasured as being about 0.0 grams per square meter per day. Accordingly,the thinning process significantly improved the breathability of thismaterial.

The hydrohead of this material prior to thinning was measured as beingin excess of 137 centimeters of water. After thinning in accordance withExample III, the hydrohead was measured as being 137. Thus, no loss ofstrength was detected by our equipment.

FIGS. 10 and 11 are two photomicrographs of the thin sheet materialwhich is area thinned in accordance with Example III. FIG. 10 is across-section of the sheet through a thinned area and FIG. 11 is a topview of a thinned area. Due to the presence of significant backgroundlight, it is difficult to discern the thinned area on cross-section.Accordingly, an arrow has been added to the photomicrograph to betterdemonstrate the degree of thinning. FIG. 12 is a scale for use withFIGS. 10 and 11 where each unit represents ten (10) microns(micrometers).

The uses to which the area thinned thin sheet material of the presentinvention may be put are numerous. Let it suffice to state that theincreased breathability of the sheet materials makes them well suitedfor barrier fabric applications.

It is to be understood that variations and modifications of the presentinvention may be made without departing from the scope of the invention.For example, in some embodiments the use of multiple ultrasonic hornsaligned abreast or sequentially may be desirable. It is also to beunderstood hat the scope of he present invention is not to beinterpreted as limited to the specific embodiments disclosed herein, butonly in accordance with the appended claims when read in light of theforegoing disclosure.

What is claimed is:
 1. A method for forming thinned areas in a thinsheet material having a thickness of about 10 mils or less wherein thearea of each of the thinned areas is generally greater than about 10square micrometers, the method comprising the steps of:(a) placing thethin sheet material on a pattern anvil having a pattern of raised areaswherein the height of the raised areas is generally less than thethickness of the thin sheet material: (b) conveying the thin sheetmaterial, while placed on the pattern anvil, through an area where afluid is applied to the thin sheet material; and (c) subjecting the thinsheet material to a sufficient amount of ultrasonic vibrations in thearea where the fluid is applied to the thin sheet material to area thinthe thin sheet material; and whereby the thin sheet material is areathinned in a pattern generally the same as the pattern of raised areason the pattern anvil.
 2. The method of claim 1, wherein the fluid isselected from the group consisting of one or more of water, mineral oil,a chlorinated hydrocarbon, ethylene glycol and a solution of 50 volumepercent water and 50 volume percent 2 propanol.
 3. The method of claim2, wherein the chlorinated hydrocarbon is selected from the groupconsisting of 1,1,1 trichloroethane and carbon tetrachloride.
 4. Themethod of claim 1, wherein the thinned areas are microareas.
 5. Themethod of claim 4, wherein the area of each of the thinned microareasgenerally ranges from at least about 10 square micrometers to about100,000 square micrometers.
 6. The method of claim 4, wherein the areaof each of the thinned microareas generally ranges from at least about10 square micrometers to about 1,000 square micrometers.
 7. The methodof claim 4, wherein the area of each of the thinned microareas generallyranges from at least about 10 square micrometers to about 100 squaremicrometers.
 8. The method of claim 1, wherein the thin sheet materialis area thinned, with a thinned area density of at least about 1,000thinned areas per square inch.
 9. The method of claim 1, wherein thethin sheet material is area thinned, with a thinned area density of atleast about 5,000 thinned areas per square inch.
 10. The method of claim1, wherein the thin sheet material is area thinned, with a thinned areadensity of at least about 20,000 thinned areas per square inch.
 11. Themethod of claim 1, wherein the thin sheet material is area thinned, witha thinned area density of at least about 90,000 thinned areas per squareinch.
 12. The method of claim 1, wherein the thin sheet material is areathinned, with a thinned area density of at least about 160,000 thinnedareas per square inch.
 13. The method of claim 1, wherein the patternanvil is selected from the group consisting of a mesh screen, a flatplate with raised areas and a cylindrical roller with raised areas. 14.The method of claim 1, wherein the thin sheet material is area thinnedonly in selected predesignated areas.
 15. The method of claim 1, whereinthe thin sheet material is subjected to at least to steps (b) and (c)more than one time.
 16. The method of claim 1, wherein the height of theraised areas is greater than the thickness of the thin sheet materialand the thin sheet material is formed from a material having aresilience such that the thin sheet material is area thinned.
 17. Amethod for forming thinned areas in a thin sheet material having athickness of from about 0.5 mil to about 5 mils wherein the area of eachof the thinned areas is generally greater than about 10 squaremicrometers, the method comprising the steps of:placing the thin sheetmaterial on a pattern anvil comprising:a heavy duty wire mesh screen; ashim plate; and a fine mesh wire screen having a pattern of raisedknuckles wherein the height of the raised knuckles is generally lessthan the thickness of the thin sheet material; conveying the thin sheetmaterial, while placed on the fine mesh wire screen, through an areawhere water is applied to the thin sheet material; and utilizing anultrasonic horn to subject the thin sheet material to a sufficientamount of ultrasonic vibrations in the area where the water is appliedto the thin sheet material to area thin the thin sheet material; andwhereby the thin sheet material is area thinned with a thinned areadensity of at least about 100,000 thinned areas per square inch in apattern generally the same as the pattern of raised knuckles on the finemesh wire screen.
 18. The method of claim 17, wherein the height of theraised areas is greater than the thickness of the thin sheet materialand the thin sheet material is formed from a material having aresilience such that the thin sheet material is area thinned.
 19. Themethod of claim 17, wherein the ultrasonic horn has a tip which isaligned, with respect to the thin sheet material, at an angle of fromabout 5 degrees to about 15 degrees.
 20. The method of claim 17, whereinthe ultrasonic horn has a tip which is aligned, with respect to the thinsheet material, at an angle of from about 7 degrees to about 13 degrees.21. The method of claim 17, wherein the ultrasonic horn has a tip whichis aligned, with respect to the thin sheet material, at an angle of fromabout 9 degrees to about 11 degrees.
 22. A method for forming thinnedareas in a thin sheet material having a thickness of from about 0.25 milto about 1 mil wherein the area of each of the thinned areas generallyranges from about 10 square micrometers to about 100 square micrometers,the method comprising the steps of:placing the thin sheet material on apattern anvil comprising:a heavy duty wire mesh screen; a shim plate;and a fine mesh wire screen having a pattern of raised knuckles whereinthe height of the raised knuckles is generally less than the thicknessof the thin sheet material; conveying the thin sheet material, whileplaced on the fine mesh wire screen, through an area where water isapplied to the thin sheet material; and utilizing an ultrasonic horn tosubject the thin sheet material to a sufficient amount of ultrasonicvibrations in the area where the water is applied to the thin sheetmaterial to area thin the thin sheet material; and whereby the thinsheet material is area thinned with a thinned area density of at leastabout 100,000 thinned areas per square inch in a pattern generally thesame as the pattern of raised knuckles on the fine mesh wire screen. 23.The method of claim 22, wherein the height of the raised areas isgreater than the thickness of the thin sheet material and the thin sheetmaterial is formed from a material having a resilience such that thethin sheet material is area thinned.
 24. The method of claim 22, whereinthe ultrasonic horn has a tip which is aligned, with respect to the thinsheet material, at an angle of from about 5 degrees to about 15 degrees.